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# SPDX-License-Identifier: Apache-2.0
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# Licensed under the Apache License, Version 2.0 (the "License");
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# http://www.apache.org/licenses/LICENSE-2.0
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from abc import ABC, abstractmethod

import torch


class RobustKernel:
    @abstractmethod
    def apply(self, x: torch.Tensor) -> torch.Tensor:
        pass


class HuberRobustKernel(RobustKernel):
    def apply(self, x: torch.Tensor) -> torch.Tensor:
        weights = torch.ones_like(x)
        s = x * x
        weights[s > 1] = 1 / torch.sqrt(s)[s > 1]
        return weights
